基于灰色系统理论的快速时序数据挖掘算法

快速时序算法是一种多目标优化的局部数据挖掘算法,处理繁杂的数据时容易陷入局部最优.为提高算法的全局数据挖掘能力,提出了一种基于灰色系统理论的快速时序数据挖掘算法.首先,该算法采用快速时序数据挖掘算法处理数据;然后,用灰色系统理论进行贪心迭代数据挖掘时,以求得更为理想的结果;最后,通过实验仿真,并与快速时序算法和MDO算法进行比较.结果表明,本文提出的数据挖掘算法具有更好的全局寻优能力,且数据挖掘效果更佳.

Submesoscale characteristics and transcription of a fatty acid elongase gene from a freshwater green microalgae, Myrmecia incisa Reisigl

Myrmecia incisa is a green coccoid freshwater microalgae, which is rich in arachidonic acid （ArA, C20： 4ω-6, △5, 8, 11, 14）, a long chain polyunsaturated fatty acid （PUFA）, especially under nitrogen starvation stress. A cDNA library of M. incisa was constructed with λ. phage vectors and a 545 nt expressed sequence tag （EST） was screened from this library as a putative elongase gene due to its 56% and 49% identity to Marchantia polymorpha L. and Ostreococcus tauri Courties et Chretiennot-Dinet, respectively. Based upon this EST sequence, an elongase gene designated MiFAE was isolated from M. incisa via 5＇/3＇ rapid amplification of cDNA ends （RACE）. The cDNA sequence was 1 331 bp long and included a 33 bp 5＇-untranslated region （UTR） and a 431 bp 3＇-UTR with a typical poly-A tail. The 867 bp ORF encoded a predicted protein of 288 amino acids. This protein was characterized by a conserved histidine-rich box and a MYxYY motif that was present in other members of the elongase family. The genomic DNA sequence of MiFAE was found to be interrupted by three introns with splicing sites of Introns I （81 bp）, II （81 bp）, and III （67 bp） that conformed to the GT-AG rule. Quantitative real-time PCR showed that the transcription level of MiFAE in this microalga under nitrogen starvation was higher than that under normal condition. Prior to the ArA content accumulation, the transcription of MiFAE was enhanced, suggesting that it was possibly responsible for the ArA accumulation in this microalga cultured under nitrogen starvation conditions.

Estimation of structural modal parameters by fourier transform with an optimal window

An adaptive Fourier Transform （FT） with an optimal window has been proposed for the time-frequency analysis of nonstationary time series. The method allows for a good estimation of both frequency and amplitude of the spectrum and can be easily applied to the general case of time-varying signals. The evaluation of the proposed approach has been performed on measured time-varying signals from a suspension bridge model and a steel frame model whose data have the typical non-stationary characteristics. The numerical results show that the proposed approach can overcome some of the difficulties encountered in the classic Fourier transform technique and can achieve higher computation accuracy.

From Sequential to Parallel Growth of Cities： Theory and Evidence from Canada

This paper examines city growth patterns and the corresponding city size distribution evolution over long periods of time using a simple New Economic Geography(NEG) model and urban population data from Canada. The main findings are twofold. First, there is a transition from sequential to parallel growth of cities over long periods of time: city growth shows a sequential mode in the stage of rapid urbanization, i.e., the cities with the best development conditions will take the lead in growth, after which the cities with higher ranks will become the fastest-growing cities; in the late stage of urbanization, city growth converges according to Gibrat′s law, and exhibits a parallel growth pattern. Second, city size distribution is found to have persistent structural characteristics: the city system is self-organized into multiple discrete size groups; city growth shows club convergence characteristics, and the cities with similar development conditions eventually converge to a similar size. The results will not only enhance our understanding of urbanization process, but will also provide a timely and clear policy reference for promoting the healthy urbanization of developing countries.

On temporal-spatial distribution of backscatter coefficients over China determined by TOPEX/Poseidon mission

This paper deals with the backscatter coefficients known as sigma0 at Ku band and C band based on the GDR-M (Merged Geophysical Data Record) of TOPEX/Poseidon (T/P) through Jan.1993 to Dec.2004 over land surface of China.After smoothing and interpolating the backscatter coefficients for both bands, we achieve the 5′×5′ grid data and the time series of backscatter coefficients in 12 years.The spatial distribution of sigma0 over typical areas (wetland, desert, mountainous area, agriculture base, etc.) of Chinese territory is analyzed and discussed.The fast Fourier transformation (FFT) is used to detect the cycles of seasonal variations of sigma0 time series and gives that the annual period is the major cycle.Meanwhile a semiannual period is also found in some places.We use the least squares method on both periods and find that the amplitude of annual period is obviously greater than that of semi-annual period.The relationship among the anomalousness of time series, variations of environment and climate change, and the serious natural calamity (flood, drought) is also discussed.Data of topography slope extracted from SRTM are used to do correlation analysis with the backscatter coefficients in parts of China to quantify the impact of slope on backscatter coefficients in Ku and C bands, and the results show that they all have a negative correlation but the magnitudes are different in different places with different coverages.Such as the area of Liaoning and Jilin has the maximum correlation -0.56, the Taklimakan Desert has the minimum correlation -0.11, and the other places commonly have correlations in (-0.3, -0.5).

Chronological constraints on multi-staged rapid cooling of the Tianshan Mountains inferred from apatite fission track analysis of modern river sands

The extreme modern elevation of the Tianshan Mountains reflects the Cenozoic deformation. Apatite Fission Track （AFI） chronometry is widely used to study the latest cooling stages caused by tectonic process or by exhumation in the uppermost crust. However, uncertainties remain over timing constraints on thermal history of the Tianshan Mountains since the Cenozoic though a great mount of dating work had been done in this area. To address this issue, modern river sands from the drainage basin on the piedmont of the Tianshan Mountains were sampled to integrate regional information. Single grains were dated with the AFT method, and then different grain-age components were identified to provide thermochronological constraints of their sources. Combined with discussion of previous dataset, our results show the multi-staged rapid cooling cluster at 46-32, 25-24, 19-13, 8-6, and -3 Ma, respectively. We interpreted these cooling events as a result of interplays between the Cenozo- ic tectonic uplift of the mountains and regional climate change.